This interestingly may actually reduce vaccinations. People are prone to viewing incentive programs for discretionary behavior as costs they can choose to pay to avoid having to engage/cease behavior. Classic example being fines for late parents at school increasing tardiness. https://twitter.com/kaitlancollins/status/1357815609136930819

Pre-fines, the penalty for parents being late in picking up their kids was social opprobrium/feeling bad. But the fines caused a lot of parents to mentally conceive of the fines as a form of paid service where they could pay the school for keeping watch over their kids later.

With Krogers here, people who might be resistant to wanting to get vaccinated may mentally view the payments for vaccinations as a form of implicit fine/pay for service. "Why are you all pressuring me, you got your $100, while I chose not to?"